428  Correspondence—MUr. C. 8S. Wilkinson—Rev. E. Hill. 
CORRESPONDENCE. 
ON THE FORMATION OF THE DIAMOND IN THE TERTIARY 
DRIFTS OF NEW SOUTH WALES,! ere. 
After referring to the recent artificial production of the diamond 
by Mr. Hannay, the writer adds: 
“When examining the New England and Mudgee Districts in 
New South Wales, I came to the conclusion, as did Mr. Norman 
Taylor also, that the diamonds (of which hundreds were found in the 
gold and tin drifts) had been chemically formed in the Miocene and 
Pliocene Cements, which are very ferruginous and sometimes siliceous, 
the waterworn pebbles being found coated with a film of silica. 
The recent alluvium only where derived from the Tertiary drifts is 
diamond-bearing; and the Tertiary drifts themselves contain 
diamonds ; but the older rocks, Silurian, Devonian, or Carboniferous, 
do not contain them, or rather, the recent alluvium derived from 
them does not, although the Tertiary drifts themselves have also 
been derived from the same Paleozoic rocks ; therefore, we can only 
conclude that the diamonds have been formed in the drifts. 
“These drifts are nearly always capped with basalt. I believe 
from the nature of the rocks that water containing some carbonate 
in solution, and also silica, was present, a chemical reaction taking 
place and setting free the carbon in a crystallized form. In the 
same way, I believe, the minute scales or crystals of graphite have 
been formed in our Hawkesbury Sandstone (Triassic). This sand- 
stone consists of (originally) rounded grains of quartz sand, coated 
now with silica in a crystallized state, and with the scales of 
graphite scattered through it. The sandstone, when broken, has 
quite a glittering appearance, from the silica coating the rounded 
grains of sand with the graphite occurring at intervals through the 
mass. J mentioned this to Prof. A. Liversidge, but he thinks the 
scales of graphite were deposited with the sand; I think not, 
however, for the sandstone, so false-bedded, etc., bears evidence of 
deposition by strong and variable currents of water, which would 
have destroyed the small graphite grains by attrition. On this 
account 1 think the graphite must have been chemically formed 
during the slow transmutation which the sandstone has undergone. 
We shall be much interested to hear of Mr. Hannay’s process for 
making the diamond.” C. S. Wiixinson, F.G.S., 
: Government Geologist for N. 8. Wales. 
ECCENTRICITY AND GLACIAL EPOCHS. 
Srr,—Mr. Greenwood’s demonstration in the July Number (p. 332) 
looks clear, but is, I think, not quite sound. The error is rather 
subtle, and not easily made out. I believe it to consist in attributing 
to the sun’s heat only the actions of melting snow and raising 
temperatures, which tacitly neglects its primary action of supplying 
the place of that heat which the earth and its atmosphere are 
1 Ina letter to R. Etheridge, Jun., dated ‘‘ Sydney, 9th April, 1880.’ 
